$(document).ready(function(){
    $('.product_edit_thumbnail').hide();
    var nImage = 1;
    $('#product_edit_show_more_thumbnail').click(function(){
        if (nImage == 5) return ;
        ++nImage;
        $('.product_edit_thumbnail#thumbnail_' + nImage).slideDown();
        if (nImage == 5) {
            $('#product_edit_show_more_thumbnail').hide();
        }
    });
});
